Hydraulic brake boosters, such as disclosed in U.S. Pat. No. 3,831,491, have been proposed for general use in vehicles because of their compactness and reliability. In such brake boosters, an input force from the operator, which is modified through a ratio changer, moves a valve to allow a proportional volume of fluid under pressure to actuate the wheel brakes of the vehicle.
In order to maintain the number of components attached to the drive train of the motor of the vehicle at a minimum, it was suggested, as disclosed in U.S. Pat. No. 3,838,629, that a portion of the output of the pump that supplies the power steering gear be diverted to operate the hydraulic brake booster.
In an effort to better utilize the space available under the hood of vehicles, U.S. patent application Ser. No. 670,513 and now U.S. Pat. No. 4,072,011 discloses a single housing for retaining both a hydraulic brake booster and a power steering gear. A flow control valve in the housing, in response to a brake actuator signal, diverts a portion of the output of the pump away from the rotary valve in the steering gear to provide the hydraulic brake booster with a power assist.
Later, as disclosed in U.S. patent application Ser. No. 832,135, a single valve was devised to operate in translatory and rotational modes to control the communication of pressurized fluid to a valve system and/or a steering system corresponding to independent operator brake and steering signals.